Input: optimize events_per_packet count calculation

This patch avoids unnecessary operations while estimating events per
packet for an input device when event type is not set.

Signed-off-by: Anshul Garg <anshul.g@samsung.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Used commit: https://github.com/Noxxxious/Zero/commit/0e302dff53f00cf113c6ab00374f52dfde1824a8